The short Hittite fragment 1086/c=KBo 20.64, currently listed among the texts related to the thunder festival under the number 631 of the Catalogue des Textes Hittites, presents some features that clearly distinguish it from the other documents collected under the same catalogue entry. It represents in my opinion what is left of an invocation ritual directed to a deity, probably to be identified with a hypostasis of the Stormgod, as the presence of the word tetḫeššar, "thunder", in the colophon seems to suggest. The text must therefore be collocated elsewhere, and I propose, in consideration of its content and structure, to place it either among the fragments of mugawar rites for the Storm-god under CTH 332 or, more generally, under CTH 459 (Fragments of mugawar). This paper presents for the first time a transcription, translation and commentary of the fragment. Interesting elements emerge from a comparison with KBo 30.119, another fragmentary tablet, erroneously classified among the fragments of festivals under CTH 670, where a similar invocation ritual seems to be described.